1. Field of the Invention
The present invention is directed to an apparatus for fastening a medical implant to a patients's bone. Specifically, a fastener is provided which can be inserted into the bone and will not back out.
2. Description of the Prior Art
It is well known to replace various parts of the human body with prosthetic implants. In one application, a prosthetic knee is used to replace a patient's damaged natural knee. In another application, a prosthetic hip is used to replace a patients's damaged hip. Both of these applications require that the implant be attached to the patient's existing bone. Normally, the implants are attached to the patient's bone by the use of fasteners through a bore in a fixation member. In some applications a polymeric articular insert is placed over the fastener and fixation member. Due to forces of varied and often great magnitude on the patient's implant, the fasteners of the prior art often back out through the bore in the fixation member and impinge into the underside of an articular insert which may cover the fixation member. This can lead to increased wear and failure of the implant caused by the head of the fastener impinging into the articular insert.
One attempted solution to the problem is to sink the head of the fastener deeper into the fixation member. This simply requires the head to move farther before it impinges into the articular insert.
The need exists for a fastener which will not back out of the fixation member and cause failure of the implant.